This invention relates to a chucking device for a dental handpiece for attaching a dental tool for dental treatment, such as a dental bur, to a head housing.
There are known various types of the chucking devices for the dental handieces, such as, for example, a chucking device described in Japanese Laid-open Patent Publication No. 1-171539 and shown herein in FIGS. 11 and 12.
In these figures, the handpiece shown therein has a foremost section 100 constituted by a head housing 103 for attaching a dental bur 102 and a head housing jacket 101 having its foremost part secured to the head housing 103. A bur tube 104 for receiving and securing the dental bur 102 therein is provided within the head housing 103.
A cover cap 107 having a central opening is fitted over an upper opening 105 of the bur tube 104 and a ring-shaped elastic locking member 106 having a slit 106a is accommodated within the upper opening 105. The elastic locking member 106 may be extended apart at the slit 106a towards both sides with the side thereof opposite to the slit 106a as a fulcrum. A positioning pin 108 implanted inwardly of the fulcrum is used for preventing excess shifting during elastic extension of the locking member 106.
An inclined cam surface 106b is formed at the inner lower end of the locking member 106. When the bur 102 is inserted into the inside of the bur tube 104, an inclined cam surface 102a at an upper engaging projection 102b of the bur 102 abuts on the inclined cam surface 106b of the elastic locking member 106 to extend the elastic locking member 106b apart. On further insertion of the bur 102 into the inside of the bur tube 104, the upper engaging projection 102b is moved past a lower inner step or shoulder 106c of the elastic locking member 106, whereby the elastic locking member 106 is reset to its original position and the projection 102b is engaged with the step 106c to secure the bur 102 within the bur tube 104.
However, in order for the elastic locking member 106 to have a predetermined strength, it is necessary for the elastic locking member 106 to be thicker than a predetermined thickness and, due to such increased thickness, there is but a little space left for the elastic locking member 106 to be extended apart within the bur tube 104. This in turn results in an extremely limited space left for the engaging projection 102b of the bur 102 to be engaged with the step 106c of the elastic locking member 106. Thus, a chucking mechanism has been desired which allows for engagement of the projection 102b of the bur 102 with the step 106c of the locking member 106 within a wider space to permit positive affixture of the bur 102 within the bur tube 104.